1. Field of the Invention
This invention relates generally to tire treads and molds, and, more specifically, to contoured tire treads and methods of forming contoured tire treads.
2. Description of the Related Art
The curing of thermoset materials such as rubber (both natural and synthetic) in molds to make elastomeric products such as tires and tire components, including tire treads, is well known. Typically, a material to be cured is placed in a mold and subjected to heat and pressure until a predetermined amount of cross-linking between molecules has been achieved. The cured article is then removed from the mold and subjected to further manipulation, such as trimming of flash from the edges of the article.
A traditional way to manufacture tire treads for retreading is to use a flat mold, wherein the tread is molded in a substantially flat or planar orientation. More specifically, a mold containing relief to form tread features extends longitudinally and laterally in a generally flat (i.e., planar) orientation to form a tread that also extends in a generally planar orientation. When retreading a tire, the tire is typically buffed, an adhesive and/or liaison rubber applied, and then the planar-formed tread is wrapped around the tire carcass. After the joint is “glued” with an adhesive, the tire is then cured in an autoclave to complete the process. The process of wrapping the flat tread onto a round tire causes the tread elements to deform as the previously planar tread is contorted about the curved periphery of the tire carcass. This deformation causes tread features, such as grooves, that run across the tread to open or expand, particularly at the tread contact surface (i.e., the road-contacting side) (see FIG. 1A), upon application to the round tire surface. A tread designer can adjust the tread design to compensate for this increase in size and shape, such as by making the feature, such as a groove, smaller or narrower, so that when it opens during application of the tread to the carcass, the feature or groove deforms or opens to its desired size and shape. Narrower tread features, such as sipes or narrow grooves, however, cannot be made smaller to open to a desired size and shape when the opening deformation is more than the desired thickness of such feature. Sipes are small slits or cuts in the blocks or ribs of a tire, introduced to provide traction edges and/or reduce the rigidity of a block or rib to improve traction and braking in wet or icy conditions or to delay irregular wear patterns. Accordingly, there is a need to provide a contoured tread, as well as means of molding a tread in a substantially flat or planar manner while still being able to obtain the desired dimensions of relatively small tread features, such as sipes.